Electron-transfer events near the reaction center in oxygen-evolving photosystem II preparations

Hoganson, Curtis W.; Babcock, Gerald T.

doi:10.1021/bi00416a005

Cited by 124 publications

(106 citation statements)

References 32 publications

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“…The magnetic interaction may consist of both isotropic exchange and anisotropic dipolar components. We note that room temperature measurements of the Yz-lineshape in intact oxygen-evolving PS II preparations show no significant broadening from the interaction with the Mn cluster (39). This is likely due to extremely rapid spin-lattice relaxation of various thermally populated spin states of the Mn cluster at this high temperature which averages out the anisotropic dipolar interaction between the cluster and Yz-.…”

Section: Methodsmentioning

confidence: 75%

Proximity of the manganese cluster of photosystem II to the redox-active tyrosine YZ.

Gilchrist

Ball

Randall

et al. 1995

Proc. Natl. Acad. Sci. U.S.A.

266

309

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Electron spin echo electron-nuclear double resonance (ESE-ENDOR) experiments performed on a broad radical electron paramagnetic resonance (EPR) signal observed in photosystem II particles depleted of Ca2+ indicate that this signal arises from the redox-active tyrosine Yz. The tyrosine EPR signal width is increased relative to that observed in a manganese-depleted preparation due to a magnetic interaction between the photosystem II manganese cluster and the tyrosine radical. The manganese cluster is located asymmetrically with respect to the symmetry-related tyrosines Yz and YD. The distance between the Yz tyrosine and the manganese cluster is estimated to be approximately 4.5 A. Due to this close proximity of the Mn cluster and the redox-active tyrosine Yz, we propose that this tyrosine abstracts protons from substrate water bound to the Mn cluster.The photosystem II (PS II) component of the plant photosynthetic apparatus oxidizes water at an oxygen-evolving complex (OEC) that consists of a tetranuclear cluster of manganese ions along with essential cofactors calcium and chloride (1). The overall architecture of PS II shows homologies to the reaction centers of the purple non-oxygen-evolving bacteria, including the C2 symmetry found in these reaction centers (2-4). In PS II this symmetry appears to persist to the sites of two important tyrosine residues, Yz (tyrosine-161 of the Dl polypeptide, with residues designated for Synechocystis sp. 6803) and YD (tyrosine-160 of the D2 polypeptide) (5-7). The Yz tyrosine serves as an electron transfer intermediate between the chargeseparating chlorophyll moiety P680 and the manganese cluster of the OEC. The symmetry-related tyrosine YD, which is typically present as a dark-stable neutral radical (YD-), is bypassed in the fast electron transfer between P680 and the OEC. Whether the Mn cluster is located on the C2 symmetry axis has been the subject of much debate. Instead, the PS II symmetry may be broken at the OEC level, locating the Mn cluster closer to the active electron transfer intermediate Yz.Calcium depletion of PS II particles by NaCl/EGTA washing (8-10) or low-pH citrate treatment (11-13) eliminates oxygen-evolving activity. In such Ca2+-depleted PS II particles, illumination at a temperature of 273 K leads to the formation of a broad (130-180 G full width at half maximum) g = 2 EPR signal. Other treatments that block oxygen evolution such as acetate or fluoride incubation lead to similar signals upon such illumination, though the signal widths vary appreciably, depending on the details of the treatment and the resulting extrinsic polypeptide composition (14-18). The broad g = 2 signal is thought to arise from a radical center, with the large linewidth caused by a magnetic interaction with the Mn cluster (18,19). UV (19) and IR (20) absorption changes in PS II that are observed concomitantly with the formation of the radical have been interpreted to favor an oxidized histidine as the origin of the broad radical signal. Alternatively, on the basis of EPR s...

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Section: Methodsmentioning

confidence: 75%

Proximity of the manganese cluster of photosystem II to the redox-active tyrosine YZ.

Gilchrist

Ball

Randall

et al. 1995

Proc. Natl. Acad. Sci. U.S.A.

266

309

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show abstract

“…Hoganson and Babcock (1988) have also observed that the amplitude of the Yz signal in O2-evolving preparations differs significantly between the experiments done with dark-adapted samples and those done with repetitively flashed samples, even in the presence of dichloro-benzoquinone and (or) ferricyanide. In steady-state flashing light (2Hz), the Yz signal amplitude has been found to amount to only 40-45% of the amplitude of the Y~ signal (Hoganson and Babcock 1988). Taking into account the small proportion of inactivated centers after each flash of the series, the oscillations with periodicity four of the fluorescence yield measured some milliseconds after each flash of a series have been reported to be correlated with the formation of an S 2 state (Delrieu and Rosengard 1988).…”

Section: Introductionmentioning

confidence: 89%

“…This conclusion is based on the finding that a small proportion of these oxygenevolving centers could become non-functional (6-10%) after each flash of a series (with a repetition rate of 1 Hz), and remain inactivated until dark-adapted (Delrieu and Rosengard 1987, 1988, 1991. Hoganson and Babcock (1988) have also observed that the amplitude of the Yz signal in O2-evolving preparations differs significantly between the experiments done with dark-adapted samples and those done with repetitively flashed samples, even in the presence of dichloro-benzoquinone and (or) ferricyanide. In steady-state flashing light (2Hz), the Yz signal amplitude has been found to amount to only 40-45% of the amplitude of the Y~ signal (Hoganson and Babcock 1988).…”

Section: Introductionmentioning

confidence: 99%

Events near the reaction center in O2 evolving PS II enriched thylakoid membranes: The presence of an electric field during the S2 state in a population of centers

Delrieu¹,

Rosengard²

1993

Photosynth Res

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Flash-induced absorption changes at 515 nm observed as a function of flash number are examined in relation to the flash-induced fluorescence yields in inside-out thylakoids. After partial dissipation of the delocalized transmembrane electric field by adding gramicidin, the analysis of period 4 oscillations and of the kinetics in the 10 ms-1 s range suggest that the variation of the absorption changes at 515 nm as a function of flash number is the result of at least two processes:1) an electric field increase related to the S2 state and 2) the fact that the field generated by the water protons inside the membrane decreases when these protons are released outside the membrane. The former field correlates with the flash-induced fluorescence yield increase induced by the donor side of Photosystem II. Both measurements show similar oscillations as a function of flash number, with maxima on the 1st, 5th and 9th flash. These oscillations, after a shift of two flashes, appear to be different from those of the O2 yield observed under similar conditions. It is proposed that, in a population of centers the electric field during the S2 state reflects the presence of a stabilized positive equivalent in the protein close to the Mn complex.

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“…An endergonic charge separation occurs between P680 and a pheophytin (Pheo) molecule. Charge recombination of the P(jgo+-PheO-pair is prevented by the following two reactions: 1) a rapid (250-550 ps, Nuijs et al, 1986;Leibl et al, 1989) electron transfer from Pheo-to a nearby plastoquinone molecule known as QA; and 2) the reduction of P680+ by a redox-active tyrosine residue (Yz) within 40-280 ns (Hoganson et al, 1988;Gerken et al, 1988). Reduced plastoquinone (QH2) carries electrons from PSII into the'cytochrome bf complex which then reduces plastocyanin (PC).…”

Section: Lumenmentioning

confidence: 99%

Structural oxidation state studies of the manganese cluster in the oxygen evolving complex of photosystem II

Liang¹

1994

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Electron-transfer events near the reaction center in oxygen-evolving photosystem II preparations

Abstract: 1985)]. This species was first observed by use of electron spin resonance to study thylakoids that had lost the ability to evolve oxygen through manganese depletion. In these preparations,

Cited by 124 publications

References 32 publications

Proximity of the manganese cluster of photosystem II to the redox-active tyrosine YZ.

Proximity of the manganese cluster of photosystem II to the redox-active tyrosine YZ.

Events near the reaction center in O2 evolving PS II enriched thylakoid membranes: The presence of an electric field during the S2 state in a population of centers

Structural oxidation state studies of the manganese cluster in the oxygen evolving complex of photosystem II

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